1. Field of the Invention
The present invention relates to projection systems having a rear projection screen, and more particularly concerns control of adverse effects of high intensity ambient light impinging on the front surface of the screen.
2. Description of Related Art
Optical projection display systems are most commonly employed for viewing in darkened areas, such as a darkened theater, for example, because of the adverse effects of reflections of ambient light. However, in many applications, such as in avionics, for example, where a display must be viewed in an open cockpit which is brightly lit by natural daylight or even sunlight, image contrast is greatly degraded. Significant difficulties have been encountered in various attempts to provide a useful image with sufficient contrast in a brightly lit environment.
Particularly in systems having a short projection length lens, various elements of the projecting optical system may be positioned so close to the rear surface of a rear projection screen that sunlight at the front face of the screen will pass through the screen to be reflected from lens elements of the projection system back through the screen. Such reflected sunlight significantly degrades contrast and viewability of the image. Anti-reflection coatings on the lens elements may decrease but cannot satisfactorily eliminate such bright ambient light reflections. For sunlight rejection absorption filters are typically used at a great cost in decreased efficiency.
Accordingly, it is an object of the present invention to avoid or minimize above mentioned problems.